1. Field of the Invention
The present invention relates to an adaptive apparatus for and method of transforming a scanning format, and more particularly, to an improved adaptive apparatus for and method of transforming a scanning format by adaptively selecting interpolation according to motion compensation and temporal-spatial time division.
2. Description of the Related Art
Recently, digitalization of information relating to multimedia has been rapidly developed. Accordingly, a compression technology of image signals has attracted considerable attention of the multimedia industry. Compression encoding and decoding enable transmission of the image signals using a low rate channel and a reduction of a requirement for a capacity of a memory storing the image signals. Therefore, the compression encoding and decoding are very important technologies in the multimedia industry requiring applications, such as a storage and transmission of the image signals.
Most of the image signals have redundancy due to auto-correlation. The redundancy is classified into temporal redundancy and spatial redundancy on a two-dimensional space. The temporal redundancy can be reduced according to motion estimation and compensation in block units, and the spatial redundancy can be reduced according to discrete cosine transform (DCT). By decreasing such redundancies, a motion pictures experts group (MPEG) can improve data compression effects of a video frame/field varied by time.
For this, it is necessary to search most similar blocks between a consecutively inputted reference frame/field and current frame/field, which is called motion estimation. In addition, a degree of a displacement in a motion of a block is called a motion vector.
In general, a block matching algorithm (BMA) is used to estimate the motion vector. The BMA compares two consecutive images, such as the reference frame/field and the current frame/field in block units, and estimates the motion on a basis of matching of signal types. According to the BMA, the motion vector is estimated by referring to the reference frame/field and the current frame/field, and motion compensation prediction is performed by using the estimated motion vector.
FIG. 1 is a block diagram illustrating a general structure of a conventional apparatus 100 for transforming a scanning format, and FIG. 2 is a diagram illustrating an image division in the conventional apparatus 100 shown in FIG. 1.
Referring to FIG. 1, the conventional apparatus 100 transforming the scanning format includes an image dividing unit 110, a motion estimating unit 120, a motion vector improving unit 130 and a motion compensation interpolating (MCI) unit 140.
The image dividing unit 110 serves to divide an external input signal into change/unchanged regions. In addition, as shown in FIG. 2, the image dividing unit 110 divides the unchanged region into covered/uncovered regions, a background, and a moving object. In FIG. 2, ‘Frame t’ denotes a current frame, ‘Frame (t−1)’ denotes a preceding frame, and ‘Frame (t+1)’ denotes a succeeding frame. Accordingly, the apparatus 100 for transforming the scanning format can apply appropriate motion compensation interpolations to each region.
FIG. 3 is a block diagram illustrating a basic structure of the motion estimating unit 120 of the conventional apparatus 100 as shown in FIG. 1.
As illustrated in FIG. 3, the motion estimating unit 120 includes a reference frame/field storing unit 122, a current frame/field storing unit 124 and a full search motion estimating unit 126. The motion estimating unit 120 estimates the motion in pixel or block units.
The reference frame/field storing unit 122 and the current frame/field storing unit 124 respectively store pixel data of the reference frame/field and the current frame/field. The pixel data of the reference frame/field and the current frame/field are used to estimate the motion vector. The full search motion estimating unit 126 estimates the motion vector in a full search method by using the frames/fields stored in the reference frame/field storing unit 122 and the current frame/field storing unit 124.
The full search method determines a search range and considers whole blocks located within a maximum displacement of the search range. That is, the full search method selects a position of the block showing a minimum matching error among the blocks as the motion vector. In the full search method, pattern matching is performed on the whole blocks of the reference frame/field and the current frame/field in the search range. As far as a real motion of the block does not exceed the search range, the full search method can search the motion vector of high accuracy.
However, when an appropriate motion vector is not searched in the full search method, visual effects are decreased as compared with the method which does not use the motion vector. In this case, the motion vector improving unit 130 must refine an inappropriate motion vector obtained in the motion estimating unit 120 according to the BMA. It is therefore possible to improve the inappropriate motion vector obtained in the motion estimating unit 120.
The MCI unit 140 searches a forward motion vector for the preceding and succeeding frames of the image to be interpolated, and performs the motion compensation and interpolation on the image. Here, the MCI unit 140 uses a simple MCI method and a linear interpolation method in block units. In the simple MCI method, the motion is searched in a local area. The searched motion is introduced to the linear interpolation method, thereby simplifying calculation of the motion compensation.
In addition, the MCI unit 140 embodies the image to be interpolated by using the estimate motion vector corresponding to the regions divided by the image dividing unit 110. That is, according to the simple MCI, the motion compensation and interpolation on the image use motion information of the adjacent images such as the preceding and succeeding frames. Accordingly, the scanning format is transformed.
However, when the size of the blocks increases, the motion estimation using the full search method fails to estimate a smooth motion vector reflecting a real motion. A predicted motion estimation method can be employed to solve the foregoing problem. However, the inappropriate motion vector is used as a candidate motion vector in the predicted motion estimation method, and thus a precise motion vector may not be searched. As a result, although the motion compensation prediction is carried out, the visual effects may be decreased as compared with the method which does not use the motion information. Moreover, the scanning format is transformed merely by the motion compensation using the motion vector. It is thus difficult to smoothly precisely perform the motion estimation.